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But Derbyshire County Council, which runs the centre, said staffing levels were "appropriate" and all adventure activities carried "an element of risk".

Jeni, who will move from Ashbrook Junior School to West Park Secondary School next month, said: "I was going across the apparatus. They said try not to touch on the grass, so I tried to step on the wooden step and then overbalanced myself.

"I hit my face on the edge of the step and screamed. There was a lot of blood and a lot of pain."

The blow knocked two of Jeni's teeth out and staff put them in a pot of milk.

But surgeons at Royal Derby Hospital could not replace them and six other broken teeth had to be removed.

Mrs Lee, of Victoria Avenue, Borrowash, said: "There was blood everywhere. They tried to wire the teeth to her gum but all the sockets were smashed to bits so they couldn't.

"She had to stay in hospital for four days and was on a drip."

Jeni is due to go back to hospital later this month, when doctors will decide what to do next. It is thought she may have to have a palate fitted.

Mrs Lee said: "Jeni is worried that when she goes to secondary school in September she will be bullied for having no teeth."

And she criticised the level of supervision at the centre, which accepts children from across Derbyshire on school trips.

Mrs Lee said: "There was nobody there to assess how she was getting off. I would have liked somebody to supervise much closer. You expect your children to come back safe."

A Derbyshire County Council spokesman said: "The safety of children visiting Lea Green is always our top priority and we're sorry that Jeni was hurt.

"We've carried out a thorough investigation following the accident which found that all proper safety measures had been carried out, the equipment had been checked, and appropriate supervision was in place.

"Lea Green has an excellent safety record but adventurous activities do carry an element of risk."